ESR1 and breast cancer: The prognosis of breast cancer depends on the histological type, size of the tumor, tumor necrosis, skin, nipple and chest wall invasion, lymphovascular invasion, grade, stage, the status of estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HER2), cell proliferation marker (ki-67), and type of therapy.